This invention relates generally to electrostatographic reproduction machines, and more particularly to a fused copy sheet distortion-removing fusing apparatus for use in such a machine to fuse toner images on sheets without image defects caused by initial heat and pressure distortion of the sheets.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith.
Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roller or to a latent image on the photoconductive member. The toner attracted to a donor roller is then deposited on a latent electrostatic images on a charge retentive surface which is usually a photoreceptor. The toner powder image is then transferred from the photoconductive member to a copy substrate or sheet. The copy substrate or sheet carrying the powder image is then moved to a heat and pressure fusing apparatus, for example, where the toner powder particles are heated in order to fuse and permanently affix them to the copy substrate or sheet.
A problem encountered with an ordinary heat and pressure fuser or fusing apparatus is that the substrate or sheet, usually a sheet of paper, distorts upon being heated within a heated fusing nip of the heat and pressure fusing apparatus. Such sheet distortion is especially pronounced in a roller type heat and pressure fusing apparatus if the heated fuser roller of such apparatus has a soft surface coating, for example of silicone rubber. In general, the distortion is also very pronounced in the case of sheets of coated paper. Such distortions cause not only undesirable fused copy sheet appearance, but also image deletions when the sheet is repassed in a duplex operation to receive a second image on the other side thereof.